Aerobic fitness, not energy expenditure, influences subsequent increase inadiposity in black and white children

Background. Low levels of energy expenditure and aerobic fitness have been hypothesized to be risk factors for obesity. Longitudinal studies to determ ine whether energy expenditure influences weight gain in whites have provid ed conflicting results. To date, no studies have examined this relationship in blacks or whether aerobic fitness influences weight gain in white or bl ack children. Methods. One hundred fifteen children, 72 white (55 girls and 17 boys) and 43 black (24 girls and 19 boys) were recruited for this study. Aerobic fitn ess, resting, total, and activity-related energy expenditure and body compo sition were measured at baseline. The children returned annually for 3 to 5 repeated measures of body composition. The influence of the initial measur es of energy expenditure and fitness on the subsequent rate of increase in adiposity was examined, adjusting for initial body composition, age, ethnic ity, gender, and Tanner stage. Because 20 children did not attain maximum o xygen consumption, the sample size for the combined analysis was 95. Results. Initial fat mass was the main predictor of increasing adiposity in this cohort of children, with greater initial fat predicting a higher rate of increase of adiposity. There was also a significant negative relationsh ip between aerobic fitness and the rate of increasing adiposity (F-1,F-82 = 3.92). With every increase of .1 L/minute of fitness, there was a decrease of .081 kg fat per kg of lean mass gained. None of the measures of energy expenditure significantly predicted increasing adiposity in white or black children. Conclusions. Initial fat mass was the dominant factor influencing increasin g adiposity; however, aerobic fitness was also a significant independent pr edictor of increasing adiposity in this cohort of children. Resting, total, or activity-related energy expenditure did not predict increasing adiposit y. It seems that aerobic fitness may be more important than absolute energy expenditure in the development of obesity in white or black children.